Memory efficient way to initialize a string to be reused inside a loop
I'm using a couple of lines in my code to be reused in a loop, and I'm wondering what would be the best way to initialize String variables to improve memory usage:
// Just for sample purposes I will declare a Map, but the same thing
// applies for an ArrayList, Database Set, etc. You get the point.
Map<String, String> sampleMap = getMap();
int mapSize = sampleMap.size();
// String initialization
String a;
String b = new String();
String c = "";
for(int i = 0; i < mapSize; i++){
a = sampleMap.get(i);
b = someFunc(a);
c = anotherFunc(a);
// Do stuff with all the Strings
}
After looping strings Strings are no longer used.
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You cannot optimize initialization or memory usage of lines in your code snippet for several reasons:
-
Java strings are immutable - you cannot change characters within a string, but you can point to a newline.
-
In your loop, the called function (for example,
aFunc()
orget()
) is responsible for highlighting the line, not the loop.
For advanced programmers: if you want to optimize the use of strings within strings of memory, you will need to use a StringBuffer / StringBuilder or raw character array and pass them around the various function calls. You have to create a buffer before the loop and pass it to get()
and other functions so that they use that one buffer instead of allocating and returning their own.
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Reduce the scope of your variables to restrict them to where they are used:
// Just for sample purposes I will declare a Map, but the same thing
// applies for an ArrayList, Database Set, etc. You get the point.
Map<String, String> sampleMap = getMap();
int mapSize = sampleMap.size();
for(int i = 0; i < mapSize; i++){
String a = aFunc();
String b = sampleMap.get(i);
String c = anotherFunc();
// Do stuff with the Strings
}
There is no performance advantage when declaring variables outside of the loop.
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I am using a couple of lines in my code to be reused in a loop
No, it is not. You are using multiple string variables that will be reused in the loop. There are no actual lines. Here's the loop body you posted:
a = sampleMap.get(i);
b = someFunc(a);
c = anotherFunc(a);
Values a
, b
and c
from previous iterations (or values before the first iteration) are completely ignored inside the loop body. Any value you assign before the loop is irrelevant at best, and distracting and / or expensive at worst. (If you use an empty string, and for some reason none of the other VMs ever use an empty string, you enter it for no reason.)
I would recommend following 6ton's guidelines and introducing variables in a loop to begin with, for readability - it won't affect your memory efficiency.
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